(1) Field of the Invention
The invention relates to the fabrication of integrated circuit devices, and more particularly, to a method of reducing substrate effects that are typically incurred by discrete passive components that are created overlying the surface of a silicon substrate.
(2) Description of the Prior Art
The creation of semiconductor devices typically starts with a monocrystalline silicon substrate, a surface region of the substrate into which the semiconductor devices are to be created is subjected to a n-type or p-type impurity implant forming n-wells or p-wells in the surface of the substrate. The n-wells or p-wells form the conductivity basis over which additional processes and implants are performed to create active functional semiconductor devices in or on the surface of the underlying silicon substrate.
Most of the processes that are performed for the creation of a semiconductor device are xe2x80x9cbest can doxe2x80x9d sequences and conditions that have over the years been refined and that provide close to the ideal required results. From this cannot be concluded that no more challenges remain in the creation of semiconductor devices or in ongoing attempts to improve the performance of these devices. Even xe2x80x9cbest can doxe2x80x9d processes leave in place conditions that restrict the reaching of the ideal conditions of device performance or implementation, major efforts of investigation will therefore continue to be aimed at eliminating these restrictions. As an example of a restriction that is imposed on device performance can be cited the creation of inductive components overlying the surface of a semiconductor surface. An energized inductor will be surrounded by electromagnetic fields, where the inductor is created on the surface of a substrate these electromagnetic fields will penetrate the surface of the substrate, thereby incurring inductive losses that reduce the performance of the inductor. Efforts to improve the performance of the inductor must therefore be aimed at reducing the electromagnetic losses incurred by the electromagnetic fields of the inductor in the surface of the silicon substrate.
The semiconductor technology continues to emphasize device performance improvements that can be achieved at competitive prices. Device performance improvements can best be accomplished by device miniaturization, which, over the years, has been made possible by continued advances of semiconductor processes and materials in combination with new and increasingly sophisticated device designs. Most semiconductor devices are aimed at processing digital data. There are however also numerous semiconductor device designs and approaches that are aimed at incorporating analog functions into devices that simultaneously process digital and analog data, or devices that can be used for the processing of analog data only. One of the major challenges encountered in the creation of analog signal processing circuitry (using digital processing procedures and equipment) is that a number of the components that are used for analog circuitry are large in size and can therefore not readily be integrated into devices that typically have feature sizes that approach the sub-micron range. The main components that offer a challenge in this respect are capacitors and inductors since both these components are, for typical analog processing circuits, of considerable size.
As an example of the benefits that can be derived can be cited the creation of an inductor. The emphasis is on the creation of an inductor of high Q value on the surface of a semiconductor substrate, using methods and procedures that are well known in the art for the creation of semiconductor devices.
A typical application for an inductor is in the field of modern mobile communication applications that make use of compact high-frequency equipment. Continued improvements in the performance characteristics of this equipment has over the years been achieved, further improvements will place continued emphasis on lowering the power consumption of the equipment, on reducing the size of the equipment, on increasing the frequency of the applications and on creating low noise levels. One of the main applications of semiconductor devices in the field of mobile communication is the creation of Radio Frequency (RF) amplifiers. RF amplifiers contain a number of standard components whereby however a major component of a typical RF amplifier is a tuned circuit that contains inductive and capacitive components. Tuned circuits form, dependent on and determined by the values of their inductive and capacitive components, an impedance that is frequency dependent, enabling the tuned circuit to either present a high or a low impedance for signals of a certain frequency. The tuned circuit can therefore either reject or pass and further amplify components of an analog signal based on the frequency of that component. The tuned circuit can in this manner be used as a filter to filter out or remove signals of certain frequencies or to remove noise from a circuit configuration that is aimed at processing analog signals. The tuned circuit can also be used to form a high electrical impedance by using the LC resonance of the circuit and to thereby counteract the effect of parasitic capacitances that are part of a circuit. One of the problems that is encountered when creating an inductor on the surface of a semiconductor substrate is that the self-resonance that is caused by the parasitic capacitance between the (spiral) inductor and the underlying substrate will limit the use of the inductor at high frequencies. As part of the design of such an inductor it is therefore of importance to reduce the capacitive coupling between the created inductor and the underlying substrate, in addition the creation of a high Q value inductor requires minimizing the electromagnetic losses incurred by the inductor.
Extensive research has been dedicated in the industry to the incorporation of RF inductors in semiconductor devices without sacrificing device performance due to substrate losses. Some of the techniques that have been used for this approach include:
the selective removing (by etching) of the silicon underneath the inductor (using methods of micro-machining) thereby removing substrate parasitic effects
using multiple layers of metal (such as aluminum) interconnects or of copper damascene interconnects
using a high resistivity silicon substrate thereby reducing resistive losses in the silicon substrate, since resistive substrate losses form a dominant factor in determining the Q value of silicon inductors
using metals that are particularly adaptable to the process of the formation of inductors; a concern is thereby however raised by the use of AlCu (a metal that is frequently used in semiconductor metallization) since AlCu has higher resistivity than gold (Au) metallization that is frequently used in GaAs technology
employing biased wells underneath a spiral conductor
inserting various types of patterned ground shields between the spiral inductor and the silicon substrate, and
creating an active inductive component that simulates the electrical properties of an inductor as it is applied in active circuitry; this approach however results in high power consumption by the inductor and in noise performance that is unacceptable for low power, high frequency applications.
The above approaches have as common objectives to:
1) enhance the quality (Q) value of the inductor
2) increase the frequency of the LC self-resonance thereby increasing the frequency range over which the inductor can be used, and
3) reduce the surface area that is required for the creation of the inductor.
Where the above has highlighted the use and implementation of an inductor in a semiconductor device, similar considerations apply to components such as a capacitor and a resistor that form part of a semiconductor device.
A principle objective of the invention is to reduce electromagnetic losses that are typically incurred by electrical components that are created on or above the surface of a silicon substrate.
Another objective of the invention is to reduce electrical interference from occurring between adjacent semiconductor devices.
Yet another objective of the invention is to reduce all detrimental influences such as eddy currents, parasitic capacitances and the like, that typically occur in a silicon surface and that negatively affect the performance of the components that are created overlying the surface of a silicon substrate.
In accordance with the objectives of the invention a new method is provided to create semiconductor devices. An unprocessed silicon substrate initially contains a first surface of raw, untreated silicon in which, in or on the surface of the substrate, semiconductor devices are created. Input/output (I/O) pads are created on the first surface of the substrate, layers of interconnect lines that connect to the I/O pads are created over the first surface of the substrate. The semiconductor devices are then protected from external influences by a layer of passivation that is deposited over the created layer of interconnect lines, I/O pads are created through the layer of passivation to the top surface of the layers of interconnect lines for further I/O connect. Passive components can be created on the surface of the layer of passivation, these passive components can be thin film passive components. The process of the invention applies an adhesive layer over the passive components and uses this layer of adhesive material to attach the completed semiconductor substrate to a glass surface. The second surface of the raw unprocessed silicon layer of the substrate underlying the passive components is now removed in addition to the silicon of the second surface of the substrate that is present between adjacent circuits. The objective of the process of the invention is to remove a maximum amount of the raw, unprocessed and loss inducing silicon, eliminating losses that are induced by the silicon substrate and as a consequence improve the quality of the passive components that overly the active surface of the substrate. By removing silicon from between adjacent circuits, interference between adjacent circuits is also eliminated.